A generator set (genset) includes a combination of a generator and a prime mover, for example a combustion engine. As a mixture of fuel and air is burned within the engine, a mechanical rotation is created that drives the generator to produce electrical power. Ideally, the engine drives the generator with a relatively constant torque and speed, and the generator accordingly produces an electrical power output having relatively constant characteristics (frequency, voltage, etc.).
Gensets are often used as a backup source of power. That is, a primary source of power such as a utility grid is typically connected to supply power for critical use, for example, to supply a hospital or a manufacturing facility with power. And, when the primary source of power fails, the genset is brought online to provide backup power for the critical use. When the primary source of power is reconnected to supply power for the critical use, the genset is returned to standby operation. Although effective, the genset cannot respond immediately to the sudden power outage or restoration. As such, without intervention, an interruption in power provided for the critical use may occur.
Gensets may be used in conjunction with an uninterruptible power supply (UPS). In most cases, the UPS stores energy by drawing power from the primary power source while the primary power source is enabled and online. In this manner, the UPS functions as an energy storage device. And, should the primary power source become disabled or disconnected, the UPS provides immediate backup power for the critical use until the genset is activated and brought up to speed, at which time the UPS may transfer load feeding responsibilities back to the genset.
Although a combined genset and UPS system may provide reliable solutions to complete power failures, the system may still experience performance fluctuations as a result of sudden load changes. That is, a load on the generator, and subsequently the engine, can be affected by external factors that can't always be precisely controlled. And, sudden changes in load can affect operation of the engine and subsequently cause undesirable fluctuations in characteristics of the generator's electrical power output.
One attempt to minimize fluctuations in characteristics of the electrical power output provided by a genset is described in U.S. Pat. No. 6,657,321 (the '321 patent) issued to Sinha on Dec. 2, 2003. The '321 patent discloses an uninterruptable power supply system having a turbine-driven generator and an energy storage system. The energy storage system is configured to supply a substantially constant DC load voltage by adjusting an amount of fuel supplied to the turbine and by adjusting an amount of supplemental DC power supplied by the energy storage system for use by the load. The energy storage system can be used to absorb and source transient power while the turbine control reacts to changes in the load. The energy storage system may comprise systems such as batteries, flywheels, superconducting magnetic energy storage systems, or combinations thereof. In one embodiment, in response to an excess in DC load voltage, the energy storage system is used to absorb excess DC power. In a more specific embodiment, the absorbing of excess DC power by the energy storage system is combined with supplying a decreased level of fuel in response to an excess in DC load voltage.
Although the system of the '321 patent may be helpful in minimizing power fluctuations in a DC power generating application, the system may be limited. That is, control based only on response to DC voltage output (excess or shortage) may be inadequate in some situations. In addition, the system of the '321 patent may be inapplicable to AC power system applications.